The present invention relates to a fan arrangement and, more particularly, to an air-circulation arrangement which reduces the noise generated by impeller blades of a rotor during their rotation.
In air-circulation arrangements, such as fans or blowers used in hair-dryers or the like, undesirable noise is generated as the impeller blades of a rotor sweep past the inlet and outlet openings provided in the housing of the air-circulation arrangement. As the air is either drawn in or discharged from the openings of the housing, it impinges along the entire length of the edge portions which bound these respective openings since the edge portions are aligned parallel to the horizontal edges of the impeller blades. Large vibrations are thereby generated which, in turn, cause the undesirable noise.
The prior art has attempted to reduce this noise, which frequently is a whistling sound, by utilizing a variety of techniques. Thus, it has been proposed to twist the impeller blades. However, this approach is very uneconomical.
It has also been proposed to unequally distribute the impeller blades on the rotor. However, this approach makes the manufacture of the rotor very expensive.
Still a further approach of the prior art has proposed to utilize porous material at the inlet opening. However, this technique has not proved to be altogether satisfactory in reducing the undesirable whistling sound.